Allocation of cache storage among applications that indicate minimum retention time for tracks in least recently used demoting schemes

ABSTRACT

A computational device receives an indication of a minimum retention time in a cache for a plurality of tracks of an application. In response to determining that tracks of the application that are stored in the cache exceed a predetermined threshold in the cache, the computational device demotes one or more tracks of the application from the cache even though a minimum retention time in cache has been indicated for the one or more tracks of the application, while performing least recently used (LRU) based replacement of tracks in the cache.

BACKGROUND 1. Field

Embodiments relate to the allocation of cache storage among applicationsthat indicate minimum retention time for tracks in least recently useddemoting schemes.

2. Background

In certain storage system environments, a storage controller (or astorage controller complex) may comprise a plurality of storage serversthat are coupled to each other. The storage controller allows hostcomputing systems to perform input/output (I/O) operations with storagedevices controlled by the storage controller, where the host computingsystems may be referred to as hosts.

The storage controller may include two or more servers, where eachserver may be referred to as a node, a storage server, a processorcomplex, a Central Processor Complex (CPC), or a Central ElectronicsComplex (CEC). Each server may have a plurality of processor cores andthe servers may share the workload of the storage controller. In a twoserver configuration of the storage controller that is also referred toas a dual server based storage controller, in the event of a failure ofone of the two servers, the other server that has not failed may takeover the operations performed by the failed server.

Data written from a host may be stored in the cache of the storagecontroller, and at an opportune time the data stored in the cache may bedestaged (i.e., moved or copied) to a storage device. Data may also bestaged (i.e., moved or copied) from a storage device to the cache of thestorage controller. The storage controller may respond to a read I/Orequest from the host from the cache, if the data for the read I/Orequest is available in the cache, otherwise the data may be staged froma storage device to the cache for responding to the read I/O request. Awrite I/O request from the host causes the data corresponding to thewrite to be written to the cache, and then at an opportune time thewritten data may be destaged from the cache to a storage device. Sincethe storage capacity of the cache is relatively small in comparison tothe storage capacity of the storage devices, data may be periodicallydestaged from the cache to create empty storage space in the cache. Datamay be written and read from the cache much faster in comparison toreading and writing data from a storage device. In computing, cachereplacement policies are used to determine which items to discard (i.e.,demote) from the cache to make room for new items in the cache. In aleast recently used (LRU) cache replacement policy, the least recentlyused items are discarded first.

U.S. Pat. No. 9,460,025 at least discusses methods for minimizingcontention among multiple threads include maintaining a plurality oflinked lists of elements. Australia Patent No. AU2015201273 at leastdiscusses a system and a method in which a currently requested item ofinformation is stored in a cache based on whether it has been previouslyrequested and, if so, the time of the previous request. U.S. Pat. No.9,734,066 at least discusses determining a workload level associatedwith an expandable data buffer, where the expandable data buffer and anexpandable mapping table cache are stored in internal memory and theexpandable mapping table cache is used to store a portion of a mappingtable that is stored on external storage. U.S. Pat. No. 8,838,903 atleast discusses a hierarchical data-storage system having a volatilestorage medium, a first non-volatile storage medium, and a controllerincluding a ranking engine tracking data writes to each of the memorymediums. U.S. Pat. No. 9,158,671 at least discusses a memory system thatincludes a nonvolatile memory having a main region and a cache region;and a memory controller having migration manager managing a migrationoperation that moves data from cache region to the main region byreferencing a Most Recently Used/Least Recently Used (MRU/LRU) list.U.S. Pat. No. 9,189,423 at least discusses a method and apparatus forcontrolling a cache. U.S. Pat. No. 6,745,295 at least discusses asystem, computer program product and method for reconfiguring a cache.

SUMMARY OF THE PREFERRED EMBODIMENTS

Provided are a method, system, and computer program product in which acomputational device receives an indication of a minimum retention timein a cache for a plurality of tracks of an application. In response todetermining that tracks of the application that are stored in the cacheexceed a predetermined threshold in the cache, the computational devicedemotes one or more tracks of the application from the cache even thougha minimum retention time in cache has been indicated for the one or moretracks of the application, while performing least recently used (LRU)based replacement of tracks in the cache. As a result, the storage ofthe cache is distributed fairly among applications that request minimumretention time for tracks in the cache.

In certain embodiments, the predetermined threshold is a predeterminedpercentage of a total number of tracks stored in the cache. As a result,the minimum retention time tracks of any application may not occupy morethan a predetermined percentage (e.g., 10%) of the cache.

In additional embodiments the plurality of tracks is a first pluralityof tracks, wherein no indication of a minimum retention time in thecache is received for a second plurality of tracks. As a result, trackswith no minimum retention time are also allowed in the cache.

In yet additional embodiments, the computational device demotes a trackof the first plurality of tracks from the cache, in response todetermining that the track is a LRU track in a LRU list of tracks in thecache and the track has been in the cache for a time that exceeds theminimum retention time. As a result, certain tracks may be stored in thecache at least for a minimum retention time indicated for the tracks.

In further embodiments, the computational device demotes a track of thesecond plurality of tracks from the cache, in response to determiningthat the track of the second plurality of tracks is a LRU track in a LRUlist. As a result, existing LRU based demotion from the cache continueto occur.

In certain embodiments, a track of the first plurality of tracks isdemoted from the cache even if the track has not been in the cache for atime that exceeds the minimum retention time, in response to determiningthat there are too many tracks that have not been in the cache for theminimum retention time or that too few tracks of the first plurality oftracks are eligible for demotion from the cache or that the applicationhas too many tracks with minimum retention time in the cache, wherein aquantitative measure of the too many tracks or the too few tracks areprovided by values of predetermined parameters. As a result, fairness incache allocation is performed concurrently with the allocation of trackswith minimum retention time in the cache.

In further embodiments, the application is a host application, whereinthe host application provides the minimum retention time for theplurality of tracks to the computational device, wherein the minimumretention time is indicative of a preference of the host application tomaintain the plurality of tracks in the cache for at least the minimumretention time, and wherein a cache management application performs anattempt to satisfy the preference of the host application to maintainthe plurality of tracks in the cache for at least the minimum retentiontime while performing the LRU based demotion of tracks in the cachewhile balancing allocation of storage in the cache among a plurality ofhost applications. As a result, fairness in practiced while allocatingminimum retention time tracks during LRU based demotion of tracks.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings in which like reference numbers representcorresponding parts throughout:

FIG. 1 illustrates a block diagram of a computing environment comprisinga storage controller coupled to one or more hosts and one or morestorage devices, in accordance with certain embodiments;

FIG. 2 illustrates a block diagram that shows demotion of tracks from anLRU list that does not incorporate a minimum retention time for selectedtracks or enforce limits on the number of minimum retention time tracksin cache for an application, in accordance with certain embodiments;

FIG. 3 illustrates a block diagram that shows the eligibility fordemotion of different types of tracks and threshold for minimumretention time tracks for an application in cache, in accordance withcertain embodiments;

FIG. 4 illustrates a flowchart that shows the addition of a track with aminimum retention time to the cache where the request for addition ismade by an application, in accordance with certain embodiments;

FIG. 5 illustrates a flowchart that shows the demote process for a trackas performed by a cache management application, in accordance withcertain embodiments;

FIG. 6 illustrates a block diagram that shows predetermined conditionsbased on which a demotion decision for a track with minimum retentiontime is made when limits are placed on the number of minimum retentiontime tracks for applications, in accordance with certain embodiments;

FIG. 7 illustrates a flowchart that shows how tracks are demoted by acache management application that incorporates minimum retention time oftracks with least recently used (LRU) based cache replacement policies,where the amount of minimum retention time tracks that an applicationmay store at a time in the cache is limited, in accordance with certainembodiments;

FIG. 8 illustrates a block diagram of a cloud computing environment, inaccordance with certain embodiments;

FIG. 9 illustrates a block diagram of further details of the cloudcomputing environment of FIG. 8, in accordance with certain embodiments;and

FIG. 10 illustrates a block diagram of a computational system that showscertain elements that may be included in the storage controller or thehost, as described in FIGS. 1-9, in accordance with certain embodiments.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanyingdrawings which form a part hereof and which illustrate severalembodiments. It is understood that other embodiments may be utilized andstructural and operational changes may be made.

A cache replacement policy in a storage controller may be LRU based. Ina conventional LRU based mechanism, a track upon being accessed is addedto a most recently used (MRU) end of a LRU list. As the track ages(i.e., is not used) the track moves to the LRU end of the LRU list andthen gets demoted (i.e., discarded or removed) from the cache.

In certain embodiments, an application may provide indications to astorage controller to store tracks used by the application for a minimumperiod of time in the cache, where the minimum period of time isreferred to as a minimum retention time. The application is likely toreaccess (i.e., access once again) the track within the minimumretention time, so it is desirable not to demote the track from thecache until the expiry of the minimum retention time. However, if theminimum retention time is strictly adhered to for all applications thencache may become full with such minimum retention tracks. As a result,the performance of applications that use the cache may be impacted.

If the minimum retention time is not specified by the application thenthe cache management application uses the conventional LRU basedmechanism to age out the track. However, if the minimum retention timeis strictly satisfied for all applications, then the cache may becomefull of tracks with minimum retention time and it is possible that notracks may be demoted. Certain embodiments handle such situations whileattempting to adhere to minimum time requirements for caching certaintracks. In such embodiments, if a track with minimum retention time isaccessed and the track moves to the LRU end of the LRU list before theminimum retention time is exceeded then instead of demoting the track,the track may be moved to the MRU end of the LRU list. If the cache isfull of tracks with minimum retention time, then some of the tracks withminimum retention time are demoted by not strictly satisfying theminimum retention time requirements. In order to ensure fairness amongvarious applications that indicate minimum retention time for tracks, ifan application has minimum retention time tracks beyond a certainpercentage of the cache then tracks for that application are demotedeven when the minimum retention time for the tracks have not beenexceeded.

Certain embodiments provide improvements to computer technology, byintegrating application indicated minimum retention time for tracks toLRU based track demoting schemes in a cache management system of astorage controller while ensuring fairness in cache allocation among aplurality of applications by restricting the amount of minimum retentiontime tracks each application may have in the cache. All applicationsthat indicate minimum retention time for tracks share the cacheequitably. As a result, caching operations in a storage controller takesaccount of hints (i.e., indications) provided by an application toretain certain tracks in cache for at least a minimum amount of timewhenever that is feasible while at the same time allocating the cachefairly among applications that request minimum retention time tracks.

Exemplary Embodiments

FIG. 1 illustrates a block diagram of a computing environment 100comprising a storage controller 102 coupled to one or more hosts 104 andone or more storage devices 106, 108, in accordance with certainembodiments.

The storage controller 102 allows the one or more hosts 104 to performinput/output (I/O) operations with logical storage maintained by thestorage controller 102. The physical storage corresponding to thelogical storage may be found in one or more of the storage devices 106,108 and/or a cache 110 of the storage controller 102.

The storage controller 102 and the hosts 104 may comprise any suitablecomputational device including those presently known in the art, suchas, a personal computer, a workstation, a server, a mainframe, a handheld computer, a palm top computer, a telephony device, a networkappliance, a blade computer, a processing device, a controller, etc. Incertain embodiments, the storage controller 102 may be comprised of aplurality of servers. The plurality of servers may provide redundancybecause if one server undergoes a failure from which recovery is notpossible, an alternate server may perform the functions of the serverthat failed. Each of the plurality of servers may be referred to as aprocessing complex and may include one or more processors and/orprocessor cores.

The storage controller 102 and the one or more hosts 104 may be elementsin any suitable network, such as, a storage area network, a wide areanetwork, the Internet, an intranet. In certain embodiments, storagecontroller 102 and the one or more hosts 104 may be elements in a cloudcomputing environment.

The cache 110 may be any suitable cache known in the art or developed inthe future. In some embodiments, the cache 110 may be implemented with avolatile memory and/or non-volatile memory. The cache 110 may store bothmodified and unmodified data, where a cache management application 112may periodically demote (i.e., move) data from the cache 110 to storagedevices 106, 108 controlled by the storage controller 102. In certainembodiments, cache management application 112 may be implemented insoftware, firmware, hardware or any combination thereof.

The plurality of storage devices 106, 108 may be comprised of anystorage devices known in the art. For example, the storage device 106may be a solid state drive (SSD) and the storage device 108 may be ahard disk drive (HDD).

A LRU list 114 is maintained in the storage controller 102 by the cachemanagement application 112. The cache management application 112receives indications from one or more host applications on whethertracks used by the host application 116 should be protected fromdemotion from the cache 110 for a time duration referred to as a minimumretention time 118. A plurality of tracks 120, 122 may have minimumretention times 124, 126 indicated by host applications. Anotherplurality of tracks 128, 130 may have no indications of minimumretention time (as shown via reference numerals 132, 134). The LRU list114 may include some of the plurality of tracks 120, 122 and some of theplurality of tracks 128, 130, i.e., the LRU list 114 includes tracks inthe cache 110 with minimum retention time and tracks in the cache 110without minimum retention time. An indicator 136 maintains the number oftracks with minimum retention time in the cache 110. It should be notedthat each track stored in the cache 110 is indicated in the LRU list114, and the LRU list 114 is used by the cache management application112 to determine which tracks to demote from the cache 110.

The storage controller 102 also includes an indicator, such as a clock,that provides the current time 138 of the storage controller 102, wherethe current time 138 and a timestamp associated with a track when thetrack is staged to the cache 110 are used to determine the amount oftime the track has been stored in the cache 110.

For each of a plurality of host applications 116 that requests minimumretention time tracks in the cache 110, the cache management application112 stores an application identifier that corresponds to the hostapplication. A plurality of application identifiers 140, 142 are shownin FIG. 1, where each application identifier is a unique identificationcorresponding to a host application (i.e., an application identifieruniquely identifies a host application). For each application identifieran indication is stored of a maximum cache allocation 144, 146 that isallowed for the corresponding host application. For each applicationidentifier another indication is stored of a number of minimum retentiontime tracks allocated (reference numerals 148, 150) in cache for thehost application. For example, for application identifier 140, themaximum cache allocation 144 may be 10000 tracks (e.g., 10% of the cache110 if the cache has 100000 tracks), and the number of minimum retentiontime tracks allocated 148 at 3 PM may be 7000 tracks. In suchembodiments, the cache management application 112 may allocate a maximumof 3000 more minimum retention time tracks for the host application inthe cache 110.

In certain embodiments, the cache management application 112 demotestracks from the cache 110 by taking into account the LRU list 114 whichis augmented with the minimum retention time for tracks where suchminimum retention times are available while at the same time ensuringthat no host application has minimum retention time tracks allocated inexcess of the maximum cache allocation for the host application. Anattempt is made by the cache management application 112 to satisfy theminimum retention time requirements to the extent possible whileensuring fairness in cache allocation among a plurality of hostapplications, while at the same time preventing the cache 110 frombecoming full

FIG. 2 illustrates a block diagram 200 that shows demotion of tracksfrom a LRU list that does not incorporate a minimum retention time forselected tracks or enforce limits on the number of minimum retentiontime tracks in cache for an application, in accordance with certainembodiments.

For simplicity, only four tracks, denoted as track K 202, track C 204,track D 206, and track B 208 are shown in FIG. 2, although a typical LRUlist may have thousands or tens of thousands of tracks.

The LRU end of the list is towards the top (as shown via referencenumeral 210). As a result, track K 202 is the least recently used track,and track B 208 is the most recently used track.

Unless minimum retention time information was included with the tracksor the number of minimum retention time tracks for an application wasrestricted, track K 202 is demoted in a conventional LRU based cachereplacement policy (as shown via reference numeral 212). However iftrack K 202 is likely to seek entry to the cache shortly after demotion(for example in a situation where a host application 116 indicates thattrack K 202 should have a minimum retention time), then the cache hitratio would be decreased.

FIG. 3 illustrates a block diagram 300 that shows the eligibility fordemotion of different types of tracks in a cache 110 and a threshold forminimum retention time tracks for an application in cache 110, inaccordance with certain embodiments.

An application identifier A 302 identifies a host application, and amaximum percentage of cache that can be allocated for tracks withminimum retention time for application identifier A 302 is 10% (as shownvia reference numeral 304). An application identifier N 306 identifiesanother host application, and a maximum percentage of cache that can beallocated for tracks with minimum retention time for applicationidentifier N 306 is 12% (as shown via reference numeral 308). As shownin FIG. 3, different application identifiers may have a differentmaximum percentage of cache that can be allocated for the applicationidentifier. The maximum percentage of cache that can be allocatedcorresponds to the maximum cache allocation 144, 146 indicated in FIG.1.

There are many tracks that are used by a plurality of host applications,and three types of exemplary tracks are shown via reference numerals310, 312, 316. Track M1 310 has no minimum retention time 312. As aresult track M1 310 is always eligible for demotion when track M1 310reaches the LRU end of the LRU list 114 (as shown via reference numeral314).

Track M2 316 has a minimum retention time 318 of 10 seconds. As a resulttrack M2 316 is eligible for demotion if track M2 316 is in cache beyond10 seconds or under certain predetermined conditions when the cache 110is in danger of getting full or when a host application corresponding totrack M2 316 exceeds its maximum cached allocation (as shown viareference numeral 320).

Track M3 322 has a minimum retention time 324 of 15 seconds. As a resulttrack M3 322 is eligible for demotion if track M3 322 is in cache beyond15 seconds or under certain predetermined conditions when the cache 110is in danger of getting full or when a host application corresponding totrack M3 322 exceeds its maximum cache allocation (as shown viareference numeral 326).

Therefore, FIG. 3 illustrates certain embodiments in which differenttracks have different minimum retention times or no retention time, andwhere different host applications may have different maximum cacheallocation for minimum retention time tracks.

FIG. 4 illustrates a flowchart 400 that shows the addition of a trackwith a minimum retention time to the cache 110 where the request foraddition is made by an application having an application identifier, inaccordance with certain embodiments. The operations shown in FIG. 4 maybe performed by the cache management application 112 that executes inthe storage controller 102. The operations shown in FIG. 4 improves theperformance of the storage controller 102 by preventing potential cachemisses should there be indications of minimum retention time 118 forcertain tracks in the cache 110 while at the same time allocating thecache fairly among all applications that have minimum retention timetracks.

Control starts at block 402 in which the cache management application112 adds the track with minimum retention time to the MRU end of the LRUlist 114. Control proceeds to block 404 in which the cache managementapplication 112 places a timestamp to indicate when the track was addedto the MRU end of the LRU list 114. The timestamp is kept in associationwith the track that is added to the LRU list 114

From block 404 control proceeds to block 406 in which the cachemanagement application 112 stores the minimum retention time of thetrack in association with the track that is added to the LRU list 114.The cache management application 112 then increments (i.e., adds thenumber 1) to the number of minimum retention time tracks 136 (as shownvia block 408).

From block 408 control proceeds to block 410 in which the cachemanagement application 112 increments the number of “minimum retentiontime tracks allocated” 148, 150 for the track corresponding to theapplication that requested the minimum retention time track.

Therefore, FIG. 4 shows certain embodiments in which tracks are added tothe LRU list 114 with indication of the minimum retention time and atimestamp that records the time at which the track was added to the LRUlist. The number of tracks with minimum retention time is updated when atrack with a minimum retention time is added to the LRU list 114. Itshould be noted that the LRU list 114 is updated each time a track isadded to the cache 110. The number of minimum retention time tracksallocated to each application identifier is also updated when a track isadded to the LRU list 114.

FIG. 5 illustrates a flowchart 500 that shows the demote process for atrack as performed ty a cache management application 112, in accordancewith certain embodiment. The operations shown in FIG. 5 improves theperformance of the storage controller 102 by reducing cache missesshould there be indications of minimum retention time 118 for certaintracks in the cache 110.

Control starts at block 502 in which the cache management application112 starts evaluating the track at the LRU end of the LRU list 114 forpotential demotion from the cache 110. Control proceeds to block 504 inwhich the cache management application 112 determines whether the trackhas a minimum retention time. If not (“No” branch 506), then the cachemanagement application 112 demotes (at block 508) the track from thecache 110.

If at block 504 the cache management application 112 determines that thetrack has a minimum retention time (“Yes” branch 510) then controlproceeds to block 512 in which the cache management application 112determines whether the difference of the current time 138 from thetimestamp of the track is greater than the minimum retention time of thetrack (i.e., whether the track has been in the cache for a time thatexceeds the minimum retention time). If so (“Yes” branch 514) then thetrack is demoted (at block 516) and the cache management application 112decrements (i.e., subtracts the number 1) the number of minimumretention time tracks 136 in the cache 110 (at block 518). The cachemanagement application 112 also decrements (i.e., reduces by 1) thenumber of minimum retention time tracks allocated for the application(as designated by the application identifier) corresponding to thedemoted track (at block 530). Therefore, the number of minimum retentiontime tracks of the application that have been allocated in the cache isdecremented on demotion of a minimum retention time track of theapplication.

If at block 512 it is determined that the difference of the current time138 from the timestamp of the track is not greater than the minimumretention time of the track (i.e., the track has not been in the cachefor a time that exceeds the minimum retention time) [“No” branch 520]control proceeds to block 522 to determine whether the track should bedemoted to prevent the cache 110 from becoming full.

At block 522 the cache management application 112 determines whetherthere are too many tracks with minimum retention time or too few tracksthat are eligible for demotion from the cache that may cause the cacheto become full or whether any application has too many minimum retentiontime tracks. What is “too many” and what is “too few” is determinedbased on certain predetermined conditions (i.e., predeterminedparameters that may be assigned to predetermined values), where someexemplary predetermined conditions are described later in FIG. 6.

If at block 522 the cache management application 112 determines thatthere are too many tracks with minimum retention time or too few tracksthat are eligible for demotion from the cache that may cause the cacheto become full or an application has too many minimum retention timetracks (“Yes” branch 524) then control proceeds to block 516 in whichthe track is demoted and the number of minimum retention time tracks isdecremented (at block 518). The cache management application 112 alsodecrements (i.e., reduces by 1) the number of minimum retention timetracks allocated for the application (as designated by the applicationidentifier) corresponding to the demoted track (at block 530).Therefore, the number of minimum retention time tracks of theapplication that have been allocated in the cache decremented ondemotion of a minimum retention time track of the application.

If at block 522 the cache management application 112 determines thatthat neither are there too many tracks with minimum retention time norare there too few tracks that are eligible for demotion from the cachethat may cause the cache to become full, nor are there any applicationthat has too many minimum retention time tracks (“No” branch 526) thenthere is no danger of the cache 110 becoming full or an applicationsecuring too much cache space, and the cache management application 112moves (at block 528) the track to the MRU end of the LRU list 114 (i.e.,the track is retained in the cache 110 and moved to the MRU end of theLRU list 114).

Therefore, FIG. 5 illustrates certain embodiments in which tracks thatare indicated as having a minimum retention time are preferred forstoring in the cache at least till the expiry of the minimum retentiontime unless the cache 110 is in danger of becoming full or anapplication for the track has too many minimum retention time tracks.

FIG. 6 illustrates a block diagram 600 that shows predeterminedconditions based on which a demotion decision for a track with minimumretention time is made, in accordance with certain embodiments.

A threshold indicating the percentage of tracks with minimum retentiontime above which tracks with minimum retention time are eligible fordemotion is maintained (as shown via reference numeral 602) in thestorage controller 102. For example in certain embodiments the thresholdmay be 50%, and as a result more if more than 50% of the tracks in thecache are tracks with minimum retention time, then one or more trackswith minimum retention time may be demoted based on the determination inblock 522 of FIG. 5.

A “maximum number” of tracks that are eligible for demotion in a“predetermined number” of tracks towards the LRU end of the LRU list 114is maintained (as shown via reference numeral 604) in the storagecontroller 102. For example, if the cache management application 112scans N tracks from the bottom of the LRU (i.e., the N least recentlyused tracks, where N is a number) and finds less than M tracks eligibleto demote because of minimum retention time requirements, then trackswith a minimum retention time may be demoted (i.e., M is the maximumnumber and N is the “predetermined number”). For example, if the cachemanagement application 112 scans 1000 tracks from the bottom of LRU(i.e., the 1000 least recently used tracks) to demote and only findsless than 100 as being eligible for demotion then tracks with minimumretention time may be demoted based on the determination in block 522 ofFIG. 5.

Another predetermined condition is that an application corresponding toa minimum retention time track has a greater than a predeterminedpercentage (e.g. 10%) of the cache filled with minimum retention timetracks. Such minimum retention time tracks are demoted wheneverpossible, to ensure fairness in cache allocation among a plurality ofapplications.

FIG. 7 illustrates a flowchart 700 that shows how tracks are demoted bya cache management application that incorporates minimum retention timeof tracks with least recently used (LRU) based cache replacementpolicies, where the amount of minimum retention time tracks that anapplication may store at a time in the cache is limited, in accordancewith certain embodiments. The operations shown in FIG. 7 may beperformed by the cache management application 112 that executes in thestorage controller 102. The operations shown in FIG. 7 improves theperformance of the storage controller 102 by preventing potential cachemisses should there be indications of minimum retention time 118 forcertain tracks in the cache 110 and also ensures fairness in cacheallocation among applications.

Control starts at block 702 in which a computational device 102 receivesan indication of a minimum retention time in a cache 110 for a firstplurality of tracks of an application 116. No indication of a minimumretention time is received for a second plurality of tracks. From block702 control may proceed in parallel to blocks 704, 706, 708.

At block 704, in response to determining that tracks of the applicationthat are stored in the cache 110 exceed a predetermined threshold (e.g.,maximum cache allocation 144) in the cache 110, the computational device102 demotes one or more tracks of the application from the cache 110even though a minimum retention time in cache has been indicated for theone or more tracks of the application, while performing least recentlyused (LRU) based replacement of tracks in the cache 110. As a result,the storage of the cache is distributed fairly among applications thatrequest minimum retention time for tracks in the cache. In certainembodiments, the predetermined threshold is a predetermined percentageof a total number of tracks stored in the cache. As a result, theminimum retention time tracks of any application may not occupy morethan a predetermined percentage (e.g., 10%) of the cache. Otherthresholds may be used in alternative embodiments.

At block 706, the cache management application 112 demotes a track ofthe first plurality of tracks from the cache 110, in response todetermining that the track is a LRU track in a LRU list of tracks in thecache 110 and the track has been in the cache 110 for a time thatexceeds the minimum retention time. As a result, certain tracks may bestored in the cache at least for a minimum retention time indicated forthe tracks.

At block 708, the cache management application 112 demotes a track of asecond plurality of tracks from the cache 110, in response todetermining that the track of the second plurality of tracks is a LRUtrack in a LRU list. As a result, existing LRU based demotion from thecache continue to occur.

Therefore, FIGS. 1-7 illustrate certain embodiments in which hints fromhost applications may indicate a minimum retention time in cache forcertain tracks used by the host applications. The storage controllerintegrates the minimum retention time into LRU based cache replacementpolicies while ensuring that limits are placed on the ability of eachhost application to use more than a certain percentage of the cache forstorage of minimum retention time tracks. Minimum retention timerequirements are satisfied whenever that is feasible without filling upthe cache while at the same time distributing the storage space of thecache in a fair manner among the plurality of applications.

Cloud Computing Environment

Cloud computing is a model for enabling convenient, on-demand networkaccess to a shared pool of configurable computing resources (e.g.,networks, servers, storage, applications, and services) that can berapidly provisioned and released with minimal management effort orservice provider interaction.

Referring now to FIG. 8 an illustrative cloud computing environment 50is depicted. As shown, cloud computing environment 50 comprises one ormore cloud computing nodes 10 with which local computing devices used bycloud consumers, such as, for example, personal digital assistant (PDA)or cellular telephone 54A, desktop computer 54B, laptop computer 54C,and/or automobile computer system 54N may communicate. Nodes 10 maycommunicate with one another. They may be grouped (not shown) physicallyor virtually, in one or more networks, such as Private, Community,Public, or Hybrid clouds as described hereinabove, or a combinationthereof. This allows cloud computing environment 50 to offerinfrastructure, platforms and/or software as services for which a cloudconsumer does not need to maintain resources on a local computingdevice. It is understood that the types of computing devices 54A-N shownin FIG. 8 are intended to be illustrative only and that computing nodes10 and cloud computing environment 50 can communicate with any type ofcomputerized device over any type of network and/or network addressableconnection (e.g., using a web browser).

Referring now to FIG. 9, a set of functional abstraction layers providedby cloud computing environment 50 (FIG. 8) is shown. It should beunderstood in advance that the components, layers, and functions shownin FIG. 9 are intended to be illustrative only and embodiments of theinvention are not limited thereto.

Hardware and software layer 60 includes hardware and softwarecomponents. Examples of hardware components include mainframes, in oneexample IBM zSeries* systems; RISC (Reduced Instruction Set Computer)architecture based servers, in one example IBM pSeries* systems; IBMxSeries* systems; IBM BladeCenter* systems; storage devices; networksand networking components. Examples of software components includenetwork application server software, in one example IBM WebSphere*application server software; and database software, in one example IBMDB2* database software. * IBM, zSeries, pSeries, xSeries, BladeCenter,WebSphere, and DB2 are trademarks of International Business MachinesCorporation registered in many jurisdictions worldwide.

Virtualization layer 62 provides an abstraction layer from which thefollowing examples of virtual entities may be provided: virtual servers;virtual storage; virtual networks, including virtual private networks;virtual applications and operating systems; and virtual clients.

In one example, management layer 64 may provide the functions describedbelow. Resource provisioning provides dynamic procurement of computingresources and other resources that are utilized to perform tasks withinthe cloud computing environment. Metering and Pricing provide costtracking as resources are utilized within the cloud computingenvironment, and billing or invoicing for consumption of theseresources. In one example, these resources may comprise applicationsoftware licenses.

Security provides identity verification for cloud consumers and tasks,as well as protection for data and other resources. User portal providesaccess to the cloud computing environment for consumers and systemadministrators. Service level management provides cloud computingresource allocation and management such that required service levels aremet. Service Level Agreement (SLA) planning and fulfillment providepre-arrangement for, and procurement of, cloud computing resources forwhich a future requirement is anticipated in accordance with an SLA.

Workloads layer 66 provides examples of functionality for which thecloud computing environment may be utilized. Examples of workloads andfunctions which may be provided from this layer include: mapping andnavigation; software development and lifecycle management; virtualclassroom education delivery; data analytics processing; transactionprocessing; and cache management mechanism 68 as shown in FIGS. 1-9.

Additional Embodiment Details

The described operations may be implemented as a method, apparatus orcomputer program product using standard programming and/or engineeringtechniques to produce software, firmware, hardware, or any combinationthereof. Accordingly, aspects of the embodiments may take the form of anentirely hardware embodiment, an entirely software embodiment (includingfirmware, resident software, micro-code, etc.) or an embodimentcombining software and hardware aspects that may all generally bereferred to herein as a “circuit,” “module” or “system.” Furthermore,aspects of the embodiments may take the form of a computer programproduct. The computer program product may include a computer readablestorage medium (or media) having computer readable program instructionsthereon for causing a processor to carry out aspects of the presentembodiments.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present embodiments may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present embodiments.

Aspects of the present embodiments are described herein with referenceto flowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instruction.

FIG. 10 illustrates a block diagram that shows certain elements that maybe included in the storage controller 102 or the host 104, or othercomputational devices in accordance with certain embodiments. The system1000 may include a circuitry 1002 that may in certain embodimentsinclude at least a processor 1004. The system 1000 may also include amemory 1006 (e.g., a volatile memory device), and storage 1008. Thestorage 1008 may include a non-volatile memory device (e.g., EEPROM,ROM, PROM, flash, firmware, programmable logic, etc.), magnetic diskdrive, optical disk drive, tape drive, etc. The storage 1008 maycomprise an internal storage device, an attached storage device and/or anetwork accessible storage device. The system 1000 may include a programlogic 1010 including code 1012 that may be loaded into the memory 1006and executed by the processor 1004 or circuitry 1002. In certainembodiments, the program logic 1010 including code 1012 may be stored inthe storage 1008. In certain other embodiments, the program logic 1010may be implemented in the circuitry 1002. One or more of the componentsin the system 1000 may communicate via a bus or via other coupling orconnection 1014. Therefore, while FIG. 10 shows the program logic 1010separately from the other elements, the program logic 1010 may beimplemented in the memory 1006 and/or the circuitry 1002.

Certain embodiments may be directed to a method for deploying computinginstruction by a person or automated processing integratingcomputer-readable code into a computing system, wherein the code incombination with the computing system is enabled to perform theoperations of the described embodiments.

The terms “an embodiment”, “embodiment”, “embodiments”, “theembodiment”, “the embodiments”, “one or more embodiments”, “someembodiments”, and “one embodiment” mean “one or more (but not all)embodiments of the present invention(s)” unless expressly specifiedotherwise.

The terms “including”, “comprising”, “having” and variations thereofmean “including but not limited to”, unless expressly specifiedotherwise.

The enumerated listing of items does not imply that any or all of theitems are mutually exclusive, unless expressly specified otherwise.

The terms “a”, “an” and “the” mean “one or more”, unless expresslyspecified otherwise.

Devices that are in communication with each other need not be incontinuous communication with each other, unless expressly specifiedotherwise. In addition, devices that are in communication with eachother may communicate directly or indirectly through one or moreintermediaries.

A description of an embodiment with several components in communicationwith each other does not imply that all such components are required. Onthe contrary a variety of optional components are described toillustrate the wide variety of possible embodiments of the presentinvention.

Further, although process steps, method steps, algorithms or the likemay be described in a sequential order, such processes, methods andalgorithms may be configured to work in alternate orders. In otherwords, any sequence or order of steps that may be described does notnecessarily indicate a requirement that the steps be performed in thatorder. The steps of processes described herein may be performed in anyorder practical. Further, some steps may be performed simultaneously.

When a single device or article is described herein, it will be readilyapparent that more than one device/article (whether or not theycooperate) may be used in place of a single device/article. Similarly,where more than one device or article is described herein (whether ornot they cooperate), it will be readily apparent that a singledevice/article may be used in place of the more than one device orarticle or a different number of devices/articles may be used instead ofthe shown number of devices or programs. The functionality and/or thefeatures of a device may be alternatively embodied by one or more otherdevices which are not explicitly described as having suchfunctionality/features. Thus, other embodiments of the present inventionneed not include the device itself.

At least certain operations that may have been illustrated in thefigures show certain events occurring in a certain order. In alternativeembodiments, certain operations may be performed in a different order,modified or removed. Moreover, steps may be added to the above describedlogic and still conform to the described embodiments. Further,operations described herein may occur sequentially or certain operationsmay be processed in parallel. Yet further, operations may be performedby a single processing unit or by distributed processing units.

The foregoing description of various embodiments of the invention hasbeen presented for the purposes of illustration and description. It isnot intended to be exhaustive or to limit the invention to the preciseform disclosed. Many modifications and variations are possible in lightof the above teaching. It is intended that the scope of the invention belimited not by this detailed description, but rather by the claimsappended hereto. The above specification, examples and data provide acomplete description of the manufacture and use of the composition ofthe invention. Since many embodiments of the invention can be madewithout departing from the spirit and scope of the invention, theinvention resides in the claims hereinafter appended.

1-25. (canceled)
 26. A method, comprising: receiving, by a computationaldevice, an indication of a minimum retention time in a cache for aplurality of tracks of an application; and in response to determiningthat tracks of the application that are stored in the cache exceed apredetermined threshold in the cache, demoting, by the computationaldevice, a track of the application from the cache even if the track hasnot been in the cache for a time that exceeds the minimum retentiontime.
 27. The method of claim 26, wherein the minimum retention time isindicative of a preference of the application to maintain the pluralityof tracks in the cache for at least the minimum retention time, andwherein a cache management application performs an attempt to satisfythe preference of the application to maintain the plurality of tracks inthe cache for at least the minimum retention time while performing LeastRecently Used (LRU) based demotion of tracks in the cache and whilebalancing allocation of storage in the cache among a plurality of hostapplications.
 28. The method of claim 26, wherein the plurality oftracks is a first plurality of tracks, and wherein no indication of aminimum retention time in the cache is received for a second pluralityof tracks.
 29. The method of claim 28, the method further comprising:demoting a track of the first plurality of tracks from the cache, inresponse to determining that the track is a LRU track in a LRU list oftracks in the cache and the track has been in the cache for a time thatexceeds the minimum retention time.
 30. The method of claim 28, themethod further comprising: demoting a track of the second plurality oftracks from the cache, in response to determining that the track of thesecond plurality of tracks is a LRU track in a LRU list.
 31. The methodof claim 28, wherein a track of the first plurality of tracks is demotedfrom the cache even if the track has not been in the cache for a timethat exceeds the minimum retention time, in response to determining thatthere are too many tracks that have not been in the cache for theminimum retention time or that too few tracks of the first plurality oftracks are eligible for demotion from the cache or that the applicationhas too many tracks with minimum retention time in the cache, wherein aquantitative measure of the too many tracks or the too few tracks areprovided by values of predetermined parameters.
 32. The method of claim26, wherein a host application provides the minimum retention time forthe plurality of tracks to the computational device, wherein the minimumretention time is indicative of a preference of the host application tomaintain the plurality of tracks in the cache for at least the minimumretention time, and wherein a cache management application performs anattempt to satisfy the preference of the host application to maintainthe plurality of tracks in the cache for at least the minimum retentiontime while performing LRU based demotion of tracks in the cache andwhile balancing allocation of storage in the cache among a plurality ofhost applications.
 33. A system, comprising: a memory; and a processorcoupled to the memory, wherein the processor performs operations, theoperations performed by the processor comprising: receiving anindication of a minimum retention time in a cache for a plurality oftracks of an application; and in response to determining that tracks ofthe application that are stored in the cache exceed a predeterminedthreshold in the cache, demoting, by the computational device, a trackof the application from the cache even if the track has not been in thecache for a time that exceeds the minimum retention time.
 34. The systemof claim 33, wherein the minimum retention time is indicative of apreference of the application to maintain the plurality of tracks in thecache for at least the minimum retention time, and wherein a cachemanagement application performs an attempt to satisfy the preference ofthe application to maintain the plurality of tracks in the cache for atleast the minimum retention time while performing Least Recently Used(LRU) based demotion of tracks in the cache and while balancingallocation of storage in the cache among a plurality of hostapplications.
 35. The system of claim 33, wherein the plurality oftracks is a first plurality of tracks, and wherein no indication of aminimum retention time in the cache is received for a second pluralityof tracks.
 36. The system of claim 35, the operations furthercomprising: demoting a track of the first plurality of tracks from thecache, in response to determining that the track is a LRU track in a LRUlist of tracks in the cache and the track has been in the cache for atime that exceeds the minimum retention time.
 37. The system of claim35, the operations further comprising: demoting a track of the secondplurality of tracks from the cache, in response to determining that thetrack of the second plurality of tracks is a LRU track in a LRU list.38. The system of claim 35, wherein a track of the first plurality oftracks is demoted from the cache even if the track has not been in thecache for a time that exceeds the minimum retention time, in response todetermining that there are too many tracks that have not been in thecache for the minimum retention time or that too few tracks of the firstplurality of tracks are eligible for demotion from the cache or that theapplication has too many tracks with minimum retention time in thecache, wherein a quantitative measure of the too many tracks or the toofew tracks are provided by values of predetermined parameters.
 39. Thesystem of claim 33, wherein a host application provides the minimumretention time for the plurality of tracks to the computational device,wherein the minimum retention time is indicative of a preference of thehost application to maintain the plurality of tracks in the cache for atleast the minimum retention time, and wherein a cache managementapplication performs an attempt to satisfy the preference of the hostapplication to maintain the plurality of tracks in the cache for atleast the minimum retention time while performing LRU based demotion oftracks in the cache and while balancing allocation of storage in thecache among a plurality of host applications.
 40. A computer programproduct, the computer program product comprising a computer readablestorage medium having computer readable program code embodied therewith,the computer readable program code configured to perform operations in acomputational device, the operations comprising: receiving, by thecomputational device, an indication of a minimum retention time in acache for a plurality of tracks of an application; and in response todetermining that tracks of the application that are stored in the cacheexceed a predetermined threshold in the cache, demoting, by thecomputational device, a track of the application from the cache even ifthe track has not been in the cache for a time that exceeds the minimumretention time.
 41. The computer program product of claim 40, whereinthe predetermined threshold is a predetermined percentage of a totalnumber of tracks stored in the cache.
 42. The computer program productof claim 40, wherein the minimum retention time is indicative of apreference of the application to maintain the plurality of tracks in thecache for at least the minimum retention time, and wherein a cachemanagement application performs an attempt to satisfy the preference ofthe application to maintain the plurality of tracks in the cache for atleast the minimum retention time while performing Least Recently Used(LRU) based demotion of tracks in the cache and while balancingallocation of storage in the cache among a plurality of hostapplications.
 43. The computer program product of claim 42, theoperations further comprising: demoting a track of the first pluralityof tracks from the cache, in response to determining that the track is aLRU track in a LRU list of tracks in the cache and the track has been inthe cache for a time that exceeds the minimum retention time.
 44. Thecomputer program product of claim 42, the operations further comprising:demoting a track of the second plurality of tracks from the cache, inresponse to determining that the track of the second plurality of tracksis a LRU track in a LRU list.
 45. The computer program product of claim42, wherein a track of the first plurality of tracks is demoted from thecache even if the track has not been in the cache for a time thatexceeds the minimum retention time, in response to determining thatthere are too many tracks that have not been in the cache for theminimum retention time or that too few tracks of the first plurality oftracks are eligible for demotion from the cache or that the applicationhas too many tracks with minimum retention time in the cache, wherein aquantitative measure of the too many tracks or the too few tracks areprovided by values of predetermined parameters.